PRACTICAL TREE SURGERY 323 



the dam which is removed when the fiUing has hardened. Asphalt and 

 asphalt mixtures promise much for the future, when the proper methods 

 of applying liquid asphalt have been discovered (Fig. 131). 



Defects in cement work are due to the use of cheap materials, 

 carelessness in the mixing of the cement, splitting of the tree by the 

 action of intense cold, dislodgment of the cement by the swaying action 

 of the wind. Cracks appear in the cement, if the wood of the tree 

 contracts away from the Ming, or by the spread of the decayed tissue 

 behind the cement work due to lack of care in excavating rotten wood 

 prior to the filling operation. These defects may cause lots of trouble. 



Metal-covered Cavities. — Sheet tin, zinc and iron have been used 

 extensively to cover cavities. These coverings often serve to exclude 

 rain, fungous organisms and destructive insects for some time. If not 

 properly applied, such tin-covered cavities are a greater menace to the 

 tree than open cavities. If such covers are used at all, the excavated 

 cavity should be thoroughly sterilized and waterproofed. The metal 

 is nailed fast with a light hammer and its center should be allowed 

 to curve outward, so as to conform to the general shape of the tree 

 trunk. The tacked edges should be as nearly air-tight and water- 

 proof as it is possible to make them, and this can be assisted by paint- 

 ing the surface of the tin. Sometimes fumigation of the cavity is 

 resorted to as an added precautionary measure. 



Where the tree is not of sufficient value to fill with cement, an open 

 cleaned cavity may be left after cauterization of the cleaned wood 

 surface and waterproofing. A layer of burned wood is sometimes a 

 sufficient protective covering, if the burning is accompHshed by one 

 of the blow lamps, such as painters use for stripping the paint off 

 woodwork. 



Guying. — Closely associated with the work of tree surgery proper, 

 and often an indispensable adjunct is the guying of limbs to prevent 

 the spHtting of the crotches, or to check further splitting. Experience 

 demonstrates the best methods of applying the hook bolts, chains or 

 other braces to the trees to be treated. This varies so widely in dif- 

 ferent trees that it is impossible to give specific directions for this 

 kind of work. 



In conclusion, it should be stated that tree surgery can be under- 

 taken safely at almost any season of the year, especially well when the 

 sap is not flowing actively, and the weather is not too cold, to freeze 



